Build Thread: An absurdly bright tent-light.

[rhd]

Each year for the past 2 decades or so, I've had an annual family canoe/camping trip to the Algonquin National Park in Ontario. Half the fun of the trip has always been the camping "gadgetry" we come up with for our excursion. We added foldable solar panels to the mix last year.

The one piece of the puzzle we've always been missing is an insanely bright tent light. Headlights are cool, and flashlights are obviously a staple, but we've wanted something that could hang from the ceiling of the tent, and essentially provide substantial reading light for the whole tent. There's probably something we could have purchased (although frankly, the options have never been quite "right").

So - time to build one!

This thread will progress over the summer as parts come in, and I start to put things together. I'll show everyone the first piece of this plan, plus explain the build concept today.

The concept is to affix 6x LED 1000 lumen emitter plates to a square piece of aluminium (PontaicG5, thanks for your help on that front!). On the flip side of that aluminium will be 4x square heatsinks with integrated fans. This assemble will hang via 4 cables from the ceiling of the tent facing downwards.

The power will be supplied by 4x 18650s. The emitters and fans both operate at 12V, and I'll be using either an LM338 or a 1084 as a linear power source. I could have gone for a buck driver in order to gain some extra efficiency...but if you haven't caught on already, this build isn't too concerned about obnoxious power usage. By my math, each set of 4x 18650s will last 25 minutes.

The power supply and batteries will be housing in an aluminium enclosure that will be on the floor inside a pelican case. The ICs will either be heatsinked to the body of that enclosure, or perhaps left on the LED ceiling assembly, depending on space constraints and heat issues. I have 5W chassis mount resistors here for the current setting, and a 3 way switch for High/Low/Off settings.

I was a bit concerned that the emitters wouldn't live up to their high output claim. However, they arrived today, and a single emitter driven at 900mA / 12V easily lit up my bathroom on par with at least a 40 incandescent.

So - the first phase of this thread may not have been the most thrilling read, but it's just the first step. Here are the emitters, more to come as this progress

 

[Cyparagon]

How big is your tent?

25 minutes isn't a lot of reading time.

That would be adequate for a medium sized room.

Have you considered automotive HID and/or lead-acid batteries?

 

[rhd]

It's a medium sized 5 person tent. There is no practical justification for the power behind this build, and thank god we're not portaging any more, because I'm going to have to canoe and carry in 32x 18650 cells (no joke - that's the plan!)

I thought about some of the other options, but LEDs + 18650s + a linear driver just felt like me - I like working with linear drivers, and the LED plates were right up my alley

 

[Lotus_Darkrose]

If that canoe caught fire that would be one hell of a viking funeral lol

 

[freeloader700]

this is going to be interesting to see. Good luck man

 

[rocket689]

Sooo, were you going to post pics of this monster? I've been curious about it ever since I gave you that source for cheap 18650's.....

 

[Flaminpyro]

Why are you using 18650s ? do you have a stock pile of em if not and you are going to be buying cells I would suggest getting 32650 cells you will need less as they are good for 10 amps each easily

 

[benmwv]

This sounds like a very cool project. I have a feeling it will sound most of it's time on low mode lol, but it always nice to have the option of the light being so bright the tent spontaneously combusts

Could you post a pic of those led's with a quarter or something? I can't really tell exactly how big they are.

Rocket, you should pm me that source

 

[jimdt7]

I cant wait for the pics ! Very cool project rhd !

 

[rhd]

Actually, the project IS done, and has been used real-world - and is really crazy

I'm making some revisions before posting the final build thread. I think I'm calling it the "Tent Melter"

 

[Kmor2004]

"Tent Melter"

Notice the name, who wants to wage he has a leaky spot in his tent?

 

[rocket689]

This sounds like a very cool project. I have a feeling it will sound most of it's time on low mode lol, but it always nice to have the option of the light being so bright the tent spontaneously combusts

Could you post a pic of those led's with a quarter or something? I can't really tell exactly how big they are.

Rocket, you should pm me that source

PM sent, Ben.

 

[Pontiacg5]

I want to know if you got any weird looks at the airport

 

[rhd]

Why are you using 18650s ? do you have a stock pile of em if not and you are going to be buying cells I would suggest getting 32650 cells you will need less as they are good for 10 amps each easily

Stock pile of 18650s?

No.

Well, that depends on your definition of stock pile. If 183 of them is a stock pile, then I guess yes, I have a stock pile

How big is your tent? 25 minutes isn't a lot of reading time.

That would be adequate for a medium sized room.

Have you considered automotive HID and/or lead-acid batteries?

Lead-acid energy density is too low to be as practical for weight-conscious camping trips.

Regarding the delay at getting photos posted, I'm doing some interesting revisions of the version I took camping. Specifically, I'm adding to this whole rig a simple USB charging port, as well as a cigarette (female) adapter. We found out mid-trip that by detaching the LED rig, and re-attaching the 18650 power source to a cigarette adapter that we had for a portable solar panal, that we could actually power standard car-accessories via a block of 4x 18650s.

The other major revision is going to be the use of multiple (10x or 12x) quad-18650 holders, wired in 4P each, instead of just one at a time. These 18650s got HOT, so I'm going to pull from multiple paralleled packs, instead of from just one.

All of this stuff is stored inside one massive pelican case.

In the end, this project has gone from an insanely bright tent light, to an all around insanely powerful emergency light and general purpose survival power source.

I'm just waiting on an order of 18650 holders from DigiKey, and then the project will get that final 4 or 5 hours of work

 

[Things]

I'm sure you know this, but please be careful with putting so many Li-Ion batteries in series! If one of them has a slightly higher internal resistance than the rest (Can be from abuse, age, different batches, or just defective batteries), it can get extremely hot and probably explode. Considering how similar tents are to rocket fuel, that's probably the last thing you want.

You should be OK as long as you charge them individually, but just be careful.

 

[rhd]

I'll be ok regarding battery heat. Why? Because I'm only going to pull ~450mA from each cell.

Why am I pulling so little from each cell? Here's why:

10x battery packs in parallel! For that photo, no flash was used, and there was no secondary light source in the room. Merely the Tent Melter clipped to my ceiling light (which itself was off at the time).

Here's a comparison with the Tent Melter clipped to my ceiling light (while running). To help make sense of what you're looking at, that's a ceiling light containing two incandescent bulbs. The Tent Melter was so bright that the camera had to adjust the exposure down. The two incandescent bulbs together still pale in comparison to the light output of this crazy contraption. I would subjectively estimate the Tent Melter on its own to illuminate an empty room with roughly twice the light output of both incandescent bulbs combined.

The project is more or less done. The light has two current modes, the "high" mode powers the LEDs at roughly 4.2A (remember, that's at roughly 14V, so about 58W), and the other "low" mode cuts it down to 1.8A (so about 25W).

The unit also has an integrated USB (5V) bucking power circuit, so that the same set of 40X cells can be used to recharge cell phones, MP3 players, etc. With roughly 100,000 mAh of power here, and even discounting for efficiency losses, I'll basically be carrying around 593 days of standby or 418 hours of straight talk time on my Android smart phone